The present invention relates to a ballast circuit for gas discharge lamps. More particularly, the present invention relates to a resistive ballast circuit particularly suitable for accepting a typical alternating current (A.C.) source of 220 volts at 50 Hz so as to develop a desired D.C. operating voltage for a gas discharge tube.
Recent improvements to the incandescent lamp art have provided an improved lighting unit having a highly efficient gas discharge tube as the main light source and an incandescent filament as a supplementary light source. Such an improved lighting unit is generally described in U.S. Pat. No. 4,350,930 of Piel et al, issued Sept. 21, 1982.
The gas discharge tube may be successfully operated by a ballast circuit developing a D.C. type operating voltage for the arc discharge tube. Such ballast circuits are as described in the previously mentioned U.S. Pat. No. 4,350,930 and also U.S. Pat. No. 4,320,325 of T. E. Anderson, issued Mar. 16, 1982.
The gas discharge tube has various modes of operation such as, (1) an initial high voltage breakdown mode, (2) a glow-to-arc transition mode, and (3) a steady state run mode. The desired operation of the arc discharge tube requires that certain circuit performance parameters of the ballast circuit be maintained for successful operation. The required circuit parameters of the ballast circuit are, among others, (1) in order to avoid lamp dropout, that is, conditions which cause the arc conditions of the gas discharge tube to extinguish so as to cause the gas discharge tube to revert from its steady state operating condition to its glow to arc mode or even to its breakdown mode, the excitation voltage applied to the ballast circuit of the gas discharge tube should always be of a value greater than the value required for the operational voltage of the gas discharge tube, and (2) the value of the difference voltage between the source voltage and the voltage applied to the gas discharge tube should always be such so as to prevent the current flowing in the gas discharge tube from dropping below a critical value, such as 60 milliamps, which if reached may cause the gas discharge tube to require a restrike voltage typically that having a value of 2.5 times that of D.C. operating voltage in order to establish the desired arc conditions of the gas discharge tube.
A further consideration for the ballast circuit for successful operation of the gas discharge tube of the improved lighting unit that should be taken into account is the ratio of the voltage applied and derived from an A.C. voltage source, between the supplementary light source filament and the primary light source efficient gas discharge tube. It is desired that the majority of voltage derived by the ballast circuit from the A.C. voltage source be applied to the primary gas discharge tube. The system efficiency of the ballast circuit may be expressed as the power delivered to the gas discharge tube divided by the power input to the ballast circuit and is desired to have a typical value of more than about 0.5. The associated circuit components along with the circuit parameter of the ballast circuit, such as one providing a D.C. operating voltage for the gas discharge tube, are selected so that a circuit efficiency of about 50 percent is achieved or exceeded.
A still further consideration is the power factor of the ballast circuit operating the gas discharge tube and incandescent filament. The power factor is commonly used as a measurement of the ratio between the total wattage consumed by a device and total line current and voltages that is made available from an A.C. power source. The power factor rating of a ballast circuit is indicative of the amount of useful work or wattage of the ballast circuit developed from the line current. The wiring capacity for carrying the current to the ballast current must be planned for the total line current that produces useful watts in addition to wasted current. In practice, for the discharge lamp considered herein, a power factor of about or exceeding 0.5 satisfies this desire.
Still further, it is desired that the lamp ballast circuit have an R.M.S. current less than or approximately in the order of the current of an incandescent lamp with comparable light output. The desired circuit efficiency and the desired power factor of the ballast circuit along with the associated values and wattage rating of the components of the ballast circuit are not maintainable if the improved lighting unit is first selected for operation of the excitation source from the typical U.S. domestic power source voltage of 120 volts, 60 cycles and then is utilized for operation with the European and elsewhere used power source voltage of 220 volts, 50 Hz. It is desired that means be provided so as to easily adapt a ballast circuit for gas discharge tubes having selected circuit relationships and associated circuit component having selected values and wattage rating relative to usage with a 120 volt, 60 Hz source so that the ballast circuit may also be used with a 220 volt, 50 Hz European power source while still maintaining both a desired circuit efficiency and a desired power factor rating for the ballast circuit.
Accordingly it is an object of the present invention to provide means that easily adapt ballast circuits selected for operation with a 120 volt, 60 Hz power source to accept and perform in a desired manner with a 220 volt, 50 Hz power source so that the gas discharge tube is successfully operated while still maintaining its desired circuit parameters of the ballast circuit.
These and other objects of the present invention will become more apparent upon consideration of the following description of the invention.